The objectives of the proposed research is to characterize all factors that are important in the pathogenesis of Pseudomonas aeruginosa and to elucidate their roles in the infectious processess. The exotoxin A is known to be the lethal toxin and development of toxoid for this toxin is one of the aim. The phospholipase C is another important toxin that account for parts of the skin lesions produced by this species. This enzyme may be the factor that account for the rapid killing effect of the organism. Purification and characterization of the phospholipase C as well as development of antisera and toxoid will be a part of this study. One of the virulence factor of Pseudomonas aeruginosa is a group of chelating agents that enable the organism to extract iron from transferrins in the sera of man and animals. These chelating agents have been termed pyochelins in our laboratory and production and characterization of these substances is also a part of this study. We are also continuing our efforts to establish an international standard for serotyping of P. aeruginosa.